INTRODUCTION The antitumor activity of norcantharidin (NCTD),the demethylated analogue of cantharidin, was studied in the early 1980s in China. NCTD has no side effects on urinary organs which cantharidin has shown and is easier to synthesize, and it can inhibit the proliferation of several tumor cell lines as well as transplanted tumors. Clinical trials with NCTD as a monotherapeutic agent indicated that NCTD had beneficial effects in patients with different kinds of digestive tract cancers, such as primary hepatoma,carcinomas of esophagus and gastric cancer, but no depressive effect on bone marrow cells. NCTD can increase the white blood cell count by stimulating the bone marrow and has some antagonistic effect against leukopenia caused by other agents. The exact cellular and molecular mechanisms of NCTD on tumor cells have not yet been elucidated to date[1-3].

免疫毒素2E8-去甲斑蝥素的研制及其体外靶向抑制效应研究

Objective The immunotoxins generated by conjugating monoclonal antibody (mAb) and a certain toxin play an important and promising role in treating hematopoietic malignancies. However, most of the toxins used for the conjugation are toxic proteins, which are immunogenic in the patients. Norcantharidin (NCTD) is a small molecule toxin without immunogenicity, and thus has become a potential new drug for hematopoietic cancers. In this study, we prepared immunotoxin 2E8-NCTD by using the ZCH-4-2E8 cells produced in the laboratory of our hospital, and then detected its targeting effect against CD+19 lymphoid malignant Nalm-6 cells in vitro.Methods 2E8 mAb was obtained from mouse ascites and purified by gel chromatography. After its purity was checked by SDS-PAGE, immunotoxin 2E8-NCTD was generated by conjugating CD19 mAb with NCTD using activated ester method. The binding activity of the immunoconjugate to CD19 antigens on cell surface, and the expression levels of the CD19 antigens on Nalm-6 and K562 cells were determined by flow cytometry. The inhibitory effects of PBS, purified 2E8 mAb, NCTD, and immunotoxin 2E8-NCTD on the cell growth of either Nalm-6 or K562 cells were then compared.Results The purity of the 2E8 mAb was higher than 99% demonstrated by SDS-PAGE assay. 2E8 mAb was detected on the surface of 99.34% of the Nalm-6 cells, while on only 0.98% of the K562. The newly generated immunotoxin had a positive rate of 99.90% on the Nalm-6 with slightly reduced binding activity. Both 2E8-NCTD and NCTD significantly inhibited the growth of CD+19 Nalm-6 cells (P < 0. 001 ), while the purified 2E8 mAb did not show any significant influences on the growth of the same cell line ( P > 0.05 ). Meanwhile, no significant inhibitory effects on the CD-19 K562 cells were identified in the 2E8-NCTD, 2E8 mAb, or control groups, indicating a significant targeting effect of 2E8-NCTD against Nalm-6 cells.Conclusions The immunotoxin 2E8-NCTD can be synthesized by activated ester method. It has target killing effects on CD+19 Nalm-6 leukemia cells in vitro.